Mana abilities are among the few activated or triggered abilities that don't use the stack or require passing priority to resolve, so they cannot be responded to or targeted. As soon as the ability goes off, the mana is created. In practice, this simply means that a player can use mana abilities any time he or she pleases, usually while playing a spell or ability and paying the cost. Other effects of the mana ability, such as the damage that sometimes happens when using Adarkar Wastes, for example, also occur immediately and can't be responded to.

Spells that generate mana, such as Seething Song, use the stack normally, and can be responded to and targeted.

605.1. Some activated abilities and some triggered abilities are mana abilities, which are subject to special rules. Only abilities that meet either of the following two sets of criteria are mana abilities, regardless of what other effects they may generate or what timing restrictions (such as “Activate this ability only any time you could cast an instant”) they may have.

605.1a An activated ability is a mana ability if it meets all of the following criteria: it doesn’t require a target (see rule 114.6), it could add mana to a player’s mana pool when it resolves, and it’s not a loyalty ability. (See rule 606, “Loyalty Abilities.”)

605.1b A triggered ability is a mana ability if it meets all of the following criteria: it doesn’t require a target (see rule 114.6), it triggers from the resolution of an activated mana ability (see rule 106.11a) or from mana being added to a player’s mana pool, and it could add mana to a player’s mana pool when it resolves.

605.2. A mana ability remains a mana ability even if the game state doesn’t allow it to produce mana.

Example: A permanent has an ability that reads “{T}: Add {G} for each creature you control.” The ability is still a mana ability even if you control no creatures or if the permanent is already tapped.

605.3. Activating an activated mana ability follows the rules for activating any other activated ability (see rule 602.2), with the following exceptions:

605.3a A player may activate an activated mana ability whenever they have priority, whenever they are casting a spell or activating an ability that requires a mana payment, or whenever a rule or effect asks for a mana payment, even if it’s in the middle of casting or resolving a spell or activating or resolving an ability.

605.3b An activated mana ability doesn’t go on the stack, so it can’t be targeted, countered, or otherwise responded to. Rather, it resolves immediately after it is activated. (See rule 405.6c.)

605.3c Once a player begins to activate a mana ability, that ability can’t be activated again until it has resolved.

605.4. Triggered mana abilities follow all the rules for other triggered abilities (see rule 603, “Handling Triggered Abilities”), with the following exception:

605.4a A triggered mana ability doesn’t go on the stack, so it can’t be targeted, countered, or otherwise responded to. Rather, it resolves immediately after the mana ability that triggered it, without waiting for priority.

Example: An enchantment reads, “Whenever a player taps a land for mana, that player adds one mana of any type that land produced.” If a player taps lands for mana while casting a spell, the additional mana is added immediately and can be used to pay for the spell.

605.5a An ability with a target is not a mana ability, even if it could put mana into a player’s mana pool when it resolves. The same is true for a triggered ability that could produce mana but triggers from an event other than activating a mana ability, or a triggered ability that triggers from activating a mana ability but couldn’t produce mana. These follow the normal rules for activated or triggered abilities, as appropriate.

605.5b A spell can never be a mana ability, even if it could put mana into a player’s mana pool when it resolves. It’s cast and resolves just like any other spell. Some older cards were printed with the card type “mana source”; these cards have received errata in the Oracle card reference and are now instants.

If a mana ability can't produce any mana, it's still legal to play the ability, but no mana will be produced on resolution.

Playing a mana ability that happens to produce no mana still counts as playing that ability. Some abilities trigger when a land is tapped for mana, and they will trigger when a land is tapped for a mana ability even if that ability generates zero mana.

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